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of purity, and whether it is natural or artificial.   The tests made are as
follows :

1.   Suspended Impurities.—These are recognised by their appearance
and are separated by fusing the product and filtering it in an oven.

2.  Mineral Matter.—From 0-5 to i gram is burnt in a platinum dish
to ascertain if anyweighable residue remains.   Any emission of odours of resin
or of burnt fats during the combustion should be noted.

3.  Solubility in Alcohol.    Reaction.—One volume of the vaseline is
shaken with two volumes of alcohol, the latter being separated and tested
as to acidity or alkalinity and diluted with water to see if it becomes turbid.

4.  Behaviour   towards   Sulphuric Acid.—10 grams of the melted
vaseline are heated with 2-5 c.c. of a mixture of 5 parts of water with 15
parts of cone, sulphuric acid on a water-bath for 15 minutes, with frequent
shaking, any browning of the acid or vaseline being noted.

5.  Detection   of Fats.—2 grams of the vaseline   are  boiled with a
few c.c. of caustic soda solution, the cold aqueous layer being subsequently
filtered off and acidified with hydrochloric acid :  turbidity or separation
of solid substance indicates the presence of fats.

6.  Detection of Resins.—By Morawski's reaction  (see Heavy Oils,
Chemical Tests, 7).

7.  Viscosity.—By  means  of  Engler's  viscometer   (see  Heavy  Oils,
Physical Tests, 7), working at 60° C. and keeping also the vessel into which
the liquid flows hot.

8.  Determination  of the  Paraffin Wax.—In a thin-walled, glass
cylinder, 20 cm. tall and 3-5 cm. wide, a weighed quantity of about 0-5
gram of the vaseline is dissolved in the hot in.3 c.c. of ether, and the solution
treated with 50 c.c. of 98% alcohol.   After being cooled to o° for an hour
and filtered through a filter also kept at o°, washing with a total quantity
of 150 c.c. of 98% alcohol maintained   at   o° (see   Figure, p. 338), the
insoluble residue is dissolved on the filter in hot benzene and the solution
evaporated in a tared glass dish and the residue weighed.    If the precipitate
formed in the tube by addition of alcohol to the ethereal vaseline solution
is not readily detached from the glass (as happens especially with natural
vaselines and with those containing ceresine), the adherent part should be

dissolved in benzene and this solution added to that previously obtained.

* *

Pure vaseline should melt to a clear liquid and should not contain mineral
matter, or dissolve appreciably in cold alcohol, or exhibit an acid or alkaline
reaction, or turn sulphuric acid brown. According to the Italian Pharma-
copoeia, pure vaseline for pharmaceutical use should be perfectly neutral and
quite free from fats, and should leave no ash.

Natural vaselines have viscosities varying from 4-5 to 7-5 at 60° C. (referred
to that of water at 20° C. and determined with the Engler apparatus), whilst
the viscosity of artificial vaselines is usually little above i and that of mixtures
of natural and artificial vaselines rarely reaches 3-5. Natural vaselines contain
63-80% of solid paraffin insoluble in alcohol, whilst the artificial ones contain
only n-35%, and mixtures of the two intermediate proportions. Ethereal
solutions of natural vaselines are precipitated by alcohol in the form of a sticky,
cheesy mass, the liquid remaining turbid ; with artificial vaselines, a flocculent
precipitate is formed, while the liquid remains clear.r.